Building a space station on the moon may seem like something out of a science fiction movie, but each new lunar mission brings that idea closer to reality. Scientists are focusing on potential lunar ice reservoirs in permanently shadowed regions, or PSRs. These are critical to establishing any form of sustainable lunar infrastructure.
In late August 2023, India’s Chandrayaan-3 lander landed on the moon’s surface in the south polar region, where scientists suspect there is ice. This landing marked an important milestone not only for India, but also for the scientific community as a whole.
For planetary scientists like me, measurements from instruments aboard Chandrayaan-3’s Vikram lander and its small six-wheeled rover Pragyan offer a tantalizing, up-close look at the parts of the moon most likely to contain ice. Previous observations have shown that ice is present in some permanently shaded areas, but estimates vary widely as to the amount, shape, and distribution of these ice deposits.
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Arctic ice deposits
My team at the Laboratory for Atmospheric and Space Physics aims to understand where the water on the moon comes from. Comets or asteroids colliding with the moon are options, as are volcanic activity and solar wind.
Each of these events leaves a distinctive chemical fingerprint, so if we can see those fingerprints, we might be able to trace them back to the source of the water. For example, sulfur is expected in higher amounts in lunar ice deposits if volcanic activity rather than comets created the ice.
Like water, sulfur is a “volatile” element on the moon because it is not very stable on the moon’s surface. It is easily evaporated and lost in space. Given its temperamental nature, sulfur is expected to accumulate only in the colder parts of the moon.
Although the Vikram lander did not land in a permanently shaded area, it measured the temperature at a high southern latitude of 69.37 degrees S and was able to identify sulfur in soil grains on the lunar surface. The sulfur reading is intriguing because sulfur may point to the source of the moon’s water.
So scientists can use temperature as a way to figure out where these types of volatiles might end up. Temperature measurements from Chandrayaan-3 could allow scientists to test models of volatile stability and find out how recently the sulfur has accumulated at the landing site.
Vikram and Pragyan are the latest in a line of spacecraft that have helped scientists study water on the moon. NASA’s Lunar Reconnaissance Orbiter was launched in 2009 and has been observing the moon from orbit in recent years. I am a co-researcher at LRO and I use its data to study the distribution, shape and abundance of water at the lunar poles.
Both India’s Chandrayaan-1 orbiter and the LRO have allowed my colleagues and me to use ultraviolet and near-infrared observations to identify ice in the permanently shadowed areas by measuring the chemical fingerprints of water. We have definitively detected water ice in the coldest shadows of the lunar poles in some of these areas, but we are still not sure why the ice is not more widespread.
On Mercury, in contrast, the permanently shadowed areas are virtually overflowing with ice. Scientists have recognized for years the need to go to the surface and make more detailed measurements of volatiles on the moon. With its sulfur detections, the Vikram lander has now taken the first tentative steps as part of a larger exploration program.
Future lunar missions
NASA has set its sights on the moon’s south pole. Leading up to the Artemis III mission to deploy astronauts to explore surface ice, the Commercial Lunar Payloads Services program will send multiple landers and rovers to search for ice later in 2023.
While there is uncertainty about the timeline of Artemis launches, the first crewed mission, Artemis II, is on track for a late 2024 or early 2025 launch, with a looping trajectory that goes behind the far side of the moon and back to the earth.
The Lunar Compact Infrared Imaging System, of which I am the principal investigator, is an infrared camera that will take temperature measurements and study the composition of the moon’s surface.
This camera, called L-CIRiS, recently underwent its final review before being delivered to NASA, and the completed flight instrument will be ready to launch on a commercial lander in late 2026.
Before L-CIRiS, the VIPER rover mission is scheduled to launch in late 2024 to the moon’s south polar region, where it will carry instruments to search for ice in microcold traps. It is believed that these small shadows, some as small as a penny, contain a significant amount of water and are more accessible than the larger PSRs.
A long-term goal of L-CIRiS and NASA’s Commercial Lunar Payload Services program is to find a suitable site for a long-term, sustainable lunar station. Astronauts could stay at this station, possibly similar to the one at McMurdo Station in Antarctica, but it would have to be somewhat self-sufficient to be economically viable. Transporting water to the moon is extremely expensive, so locating the station near ice reservoirs is a must.
During the Artemis III mission, NASA astronauts will use information collected by the Commercial Lunar Payload Services program and other missions, including Chandrayaan-3, to assess the best locations to collect samples. The temperature and composition measurements of Chandrayaan-3 and L-CIRiS are comparable to those required for the success of Artemis. Cooperation between space agencies, young and old, will thus be an important feature of a long-term, sustainable human presence on the moon.